Tagging systems that track vehicles have been devised. These tagging systems may include tagging devices, such as radio frequency (RF) tags or chemical tags that may be sprayed onto the vehicle's outer surface. These tagging devices may be detected by detectors over a period of time to monitor the location of the vehicle.
Radio frequency tags have a problem in that instruments may be used that allow the vehicle occupants or others to sweep the vehicle for the presence of these tags. These instruments may detect the presence of radio frequency tags due to one of several electromagnetic effects common to all radio frequency tags.
Chemical tags are similarly prone to detection by vehicle occupants or others not intended to detect the tag. One example of a chemical tag includes quantum dot devices dispersed in a solvent mixture that may be sprayed onto the vehicle's outer surface. When dried, the quantum dots may fluoresce at a particle optical frequency that can be detected by a remote optical detector. Quantum dots are dark in appearance, however, which may be relatively difficult to conceal on lightly colored vehicles. Other chemical tags may similarly have a distinctive color, may noticeably disturb dust or dirt when applied, or may otherwise be too readily detectable by the naked eye.
Current chemical tags for the outside of vehicles also suffer from the retention problems. Washing the vehicle may remove most or all of the taggant material.